Patent GB-704850-A (GB)
Title: Improvements in and relating to hydraulic speed responsive systems
Inventor: DAVIES DAVID OMRI
IPC: F02C9/28
Filed: 1949-12-07
Abstract: 704,850. Gas turbine plants; jet propulsion plants. ROLLS-ROYCE, Ltd. Dec. 1, 1950 [Dec. 7, 1949], No. 31458/49. Class 110 (3). [Also in Group XXIX] A hydraulic speed-responsive system which is particularly adapted to perform control functions associated with the operation of a prime mover such as a gas turbine comprises two flow restricting devices 61, 65, Figs. 2, 4, through which the flow from a positive-displacement fixed capacity pump 64 driven by the prime mover passes, one 65 of the flow restricting devices offering a greater restriction to fluid flow than the other, and pressureresponsive means responsive to the pressure drops created by the two flow restricting devices, byepass means being provided for the flow-restricting device 65 which offers the greater resistance to prevent the pressure drop created thereby from becoming excessive at high rotational speeds of the prime mover. The pressure-responsive means which is adapted to effect the control function to be performed may be constituted as a single pressureresponsive device on which the pressure differences created by the flow-restricting devices act selectively, or as two pressureresponsive devices one for each flow-restricting device. In the case where two pressure-responsive devices are employed, these may effect the same control function over different speed ranges, thereby achieving greater sensitivity in regulation in the lower speed range or they may effect different control functions. Either or both of the flow restricting devices may be of the kind in which the pressure drop created thereby is directly proportional to the fiuid flow and therefore to the speed of the prime mover. The flow restrictor 65 is of this kind and comprises a spring-pressed valve 66 cooperating with an orifice 68. In Fig. 2 the hydraulic speedresponsive means is adapted to control the incidence of the stator blades 14 of an axial flow compressor in a gas turbine engine in the high speed range and a fuel valve 93 adapted to bye-pass fuel round the main throttle 21 during starting, in the low speed range. The fuel injectors 15a are fed from an engine driven pump 19 having a suction pipe 18 and a delivery pipe 20 containing the throttle 21 and a shut-off cock 22. The pump 64 also draws fluid from the pipe 18 and pumps it round a loop 60 containing the two flow restrictors 61, 65. The bye-pass means for the restrictor 65 comprises a spring-loaded relief valve 70 normally closing an orifice 72 and designed to prevent any substantial increase in the pressure drop across the restrictor 65 once the valve 70 opens. The stator blades 14 are operated by a servo-piston 32 opposite ends of which are supplied with fluid from the pump 19 by a pipe 39 and passages 40, 41 of which the passage 41 contains a restriction 42. Due to the aperture 36 in the hollow piston rod 32a, different areas of the piston are exposed to fluid pressure on its opposite sides. The pressure in the space 37 on the right hand side of the piston 32 is under the control of a leak-off valve 54 controlling a passage 55 and operated by a spring-loaded diaphragm 45 subject to the pressure drop across the restricted orifice 61. On movement of the piston 32, the valve 54 is reset by a spring 40. The byepass valve 93 is opened against a spring 94 by a solenoid 92 in circuit with two fixed contacts 90 and a movable bridge contact 91 supported by a rod 77 connecting two diaphragms 75, 76. The latter divide a cylinder 74 into three spaces 78, 79, 80 of which the centre space containing the contacts 90, 91 is connected to atmosphere and the end spaces 78, 80 are connected upstream and downstream of the flow restrictor 65 respectively. The pressure difference acting on the diaphragms overcomes a spring 84 before the contacts 90, 91 engage and the valve 93 opens. The contacts remain in engagement until the pressure difference is sufficient to overcome a further spring 85 normally engaging an abutment 87. The bye-pass valve 93 is thus open for an intermediate part only of the lower speed range. In Fig. 3, the stator blades 14 of the compressor are controlled throughout the whole speed range; in the lower speed range by the restrictor 165 the pressure drop across which acts on a spring loaded diaphragm 245, and in the higher speed range bv the restrictor 161 the pressure drop across which acts on a diaphragm 145. The restrictor 165 offers a greater resistance to fluid flow and has a bye-pass relief valve 70 as in Fig. 2. The diaphragms 145, 245 respectively control servopistons 132, 232 as in Fig. 2 and the servo-pistons act on the linkage 28 operating the stator blades through a floating lever 27. In Fig. 4, the stator blades 14 of the compressor are controlled by a single spring-loaded diaphragm 45 through a servomotor 30 as in Fig. 2. The diaphragm 45 is subject to the pressure drop across the flow restrictor 61 or the flow restrictor 65 according to the position of change-over valves 98, 99. The latter are linked together and moved from one position to the other against a spring load by a solenoid 102 in circuit with a pressure responsive switch 101 which operates to disconnect the diaphragm 45 from the flow restrictor 65 and connect it to the restrictor 61 when the pressure drop across the restrictor 65 is a fixed margin below that at which the bye-pass valve 70 is arranged to open. Hydraulic speed-responsive systems of the kind described may be used to control the fuel supply to a prime mover or in the case of a gas turbine engine to adjust the nozzle guide vanes of the turbine or the effective area of the propulsion nozzle. Specification 704,849 is referred to.